(a) Field of the Invention
This invention relates in general to an electrophotographic element, and in particular to a multilayered electrophotographic element comprising a conductive substrate, a charge generation layer and a charge transport layer adjacent the charge generation layer.
(b) Description of the Prior Art
A plurality of multilayered electrophotographic elements comprising, in successive layers; a conductive substrate, the so-called charge generation layer (CGL) capable of generating a charge (which is called a carrier, too) by light absorption and the so-called charge transport layer (CTL) capable of transporting a charge generated by CGL by virtue of the force of an electric field, wherein the positional relation between the CGL layer and the CTL layer may be reversed and both said layers are each designed to achieve its own separate function, have hitherto been proposed and some of them are already put to practical use.
It is generally considered that a charge generation layer must be formed uniformly, extremely thin and smoothly in order to improve the electrophotographic characteristics such as electrostatic characteristics, image characteristics and so forth in the above mentioned multilayered electrophotographic elements.
The following are well known as the processes for the formation of a charge generation layer, for instance, such as (1) evaporating deposition of a charge generation material such as Se, selenium alloy, organic pigment or the like (Japanese Laid-open Patent Application No. 47838/1973, Japanese Laid-open Patent Application No. 48334/1974, etc.), (2) coating and drying of a dispersion obtained by dispersing a charge generation material such as Se, selenium alloy, inorganic pigment, organic pigment or the like in a binder (Japanese Laid-open Patent Application No. 18543/1972, etc.), (3) coating of a solution obtained by dissolving a charge generation material such as organic pigment in an organic amine (Japanese Laid-Open Patent Application No. 55643/1977, etc.) and so forth.
The aforesaid process (1) can surely form a uniform, extremely thin layer but it is defective in that it leads to the high cost of equipment and encounters difficulties in production control. Further, the evaporation depositable charge generation materials to be used therefor are limited in selection and so forth. The aforesaid process (2) is surely easy to perform as well as being advantageous in the cost aspect because the various dispersing and coating techniques have already been established, but the dispersibility and dispersion stability of the dispersion per se are called into question in order to obtain an extremely thin layer in a stable manner. The aforesaid process (3) is also easy to perform for the same reason as mentioned with reference to the above process (2), but it still involves troubles in the safety and stability of the solution per se, and further it is defective in that said process leads to high cost and high equipment cost.